This invention relates to an analog switch, and more particularly to an analog switch for switching a signal by opening and closing a bias circuit for an amplifier involved.
Conventional analog switches of the type referred to have comprised a feedback amplifier having a positive input to which a signal to be switched and a bias voltage are applied. During the application of a control signal in form of a rectangular pulse applied thereto, the feedback amplifier has been put in its closed position to deliver the signal superposed on the bias voltage to its output. However, in the absence of the control signal, the feedback amplifier has been in its open position to prevent the signal from being developed at its output. Conventional analog switches as described above have been very excellent in that the input impedance in operation is very high and the distortion factor is very small. However, they may generate transient noise during the switching because of the fact that the operating voltage in its open position is much different from the bias voltage. That transient noise offends the ear particularly in the case of audio equipment which must have low transient.
Accordingly, it is an object of the present invention to provide a new and improved analog switch for switching a signal with a small distortion factor and which is still free from transient noise generated upon switching.